Effect Of Spent Mushroom Substrate And Composted Spent Mushroom Substrate On Remediation Of Black Soil And Red Soil Polluted By Lead

As one of the earliest metals used by human beings,Lead has been defined as a highly toxic environmental and neurotoxic substance by the World Health Organization(WHO).Along with the development of China’s industry,lead-containing pollutants enter the soil through various ways,which not only causes environmental pollution,but also threatens human health.The in-situ remediation method based on agricultural solid waste has the advantages in low cost,high efficiency and environmental friendliness,and has a good application prospect in soil heavy metal treatment.In this study,the waste substrate from edible fungi industry-Spent mushroom substrate(SMS)and its composted spent mushroom substrate(CSMS)were used to remediate the lead-contaminated soil in situ.The biosorption properties were characterized by specific surface area,Scanning electron microscope and energy spectrometer(SEM-EDX),Fourier infrared spectrophotometer(FTIR),X-ray diffractometer(XRD),water contact angle and cation exchange amount analysis.The biosorption conditions and mechanisms of lead were investigated by batch test,dynamic monitoring test and isothermal model fitting.In the simulated remediation experiments with black soil and red soil,the changes of water,air porosity,p H and EC were fully considered.The transformation law and spatial mobility characteristics of lead in soil were compared in detail.The bulk density,freezing and thawing factors were also initially explored.In addition to considering the above indicators,the three restoration planting experiments(pot experiment,floating island hydroponic test and frame planting test)also revealed the effects of bacillary repair agents on soil enzyme activities and soil bacterial community diversity from the perspective of rhizosphere microecology.In terms of the effects on p lants,in addition to the conventional yield indicators,the adsorption of lead by root surface was compared,and the effect of repair on photosynthetic center damage was compared by chlorophyll fluorescence induction kinetics.This study confirmed the application potential of SMS and CSMS in biosorption and soil heavy metal pollution remediation,and pointed out the possible problems,and explored a new way for the utilization of this kind of biomass.The main conclusions of this study are as follows:1.SMS is a good biological adsorbent,which can effectively adsorb lead ions in water.Composting can change the functional groups and basic properties of SMS,and improve the removal ability of lead ions from three aspects: p H,cation exchange capacity and h ydrophilicity.SMS removes lead ion from water conventional mainly by biosorption,while CSMS mainly depends on precipitation except biosorption.2.The initial p H value of lead solution greatly affects the removal efficiency.The removal rate of lead by SMS increases with the increase of p H.The removal rate of lead by CSMS is the highest at p H 3.The composting treatment can increase the removal rate of lead ions,save the amount of biosorbent,and increase the removal rate at the initial concentration se t by all experiments.Monitoring the lead solution and corresponding lead-free water of CSMS and SMS helps to understand the biomass properties,the removal mechanisms and processes under batch experiment.The removal ability of the graded samples after crushing and sieving generally increases with the decrease in the particle size.When the initial concentration of lead ion is known,a monitoring model based on p H and EC values is established.The two models can be used to quickly and effectively detect the removal effect of heavy metal lead.3.In the simulation test of lead-contaminated soil remediation,it has been found that effect of CSMS better than that of SMS.The addition of both remediation agents can increase the p H of black soil and red soil.CSMS increases the EC value of both soils.SMS reduced the EC value of black soil and had little effect on that of red soil.After 50 days of culture,the types of the functional groups in the two soils amended with the remediation agents were similar to tho se of the original soil.The remediation agents can greatly reduce the exchangeable lead content in red soil and reduce the overall mobility of lead.The exchangeable lead content in black soil is low,and the morphological transformation is not obvious at the pollution level of 600 mg/kg.4.Under potted black soil conditions,CSMS makes the soil more humid and its own salinity can increase soil EC.Exogenous organic matter and high water content work together to lower the soil p H and weaken the redox reaction intensity,so that the carbonate-bound lead and iron-manganese oxides are significantly lower than those in the original soil and SMS-added soil.The addition of SMS can make the soil more loose and breathable,and enhance the alternation of drying and wetting,and accelerate the mineralization of organic components.The decomposition of SMS increase the soil p H,and the biosorption,complexation and other effects on lea d reduce the soil conductivity.SMS stimulates soil microbial activity and enhances soil respiration.Both CSMS and SMS can reduce the activity of catalase.The addition of SMS reduced the bacterial flora richness of lead-contaminated and non-contaminated soils.The effects of adding CSMS on soil bacterial populations of lead-contaminated and non-contaminated was not significant,while that of SMS was significant.The two remediation agents had different influence on the composition of several major phylum.At the genus level,the soil community composition with the same remediation agent was similar.The difference between lead contaminated and non-contaminated samples of the same remediation agent was obvious.The effects of remediation agents on some microbial populations are significantly correlated with changes in environmental conditions.CSMS may have a negative impact on seeding emergence,while SMS may promote emergence.CSMS can promote the growth of water spinach and increase the yield.The application of SMS may cause nitrogen deficiency in plants.The application of CSMS can alleviate the damage of chlorophyll photosynthetic center of leaves under lead pollution,and make plants grow better.SMS can also reduce the damage of photosynthetic system under the pollution of lead nitrate.In the absence of lead nitrate,the decomposition of SMS consumes the available nitrogen in the soil,and plant nitrogen deficiency affects photosynthesis,resulting in a reduced biomass.5.In the hydroponics experiment of floating islands,the two remediation agents have little effect on the transformation of lead form in rhizosphere of black soil,but promoted the decrease of available lead and the increase of organic bound lead in rhizosphere of red soil.CSMS reduced the proportion of exchangeable lead in red soil by 72.8%,and increased the prop ortion of organic bound lead by 98.1%.SMS reduced the proportion of exchangeable lead in red soil by 68%,and increased the proportion of organic bound lead by 79.2%.At the same time,the p H buffering capacity,EC value and yield of water spinach in rhizosphere soil were increased by both remediation agents.In frame planting experiment,the organic bound state of lead in rhizosphere black soil of water spinach increased slightly with two kinds of remediation agents.The proportion of exchangeable lead in rhizosphere red soil decreased by 86.2% and the proportion of organic bound lead increased by 93.6% by CSMS remediation agent(p < 0.05).The proportion of exchangeable lead in rhizosphere red soil decreased by 80.6% and that of organic bound lead increased by 64.7% by adding SMS(p < 0.05).With the growth of plants,both types of rhizosphere soil acidified,while the soil p H value increased significantly.CSMS increased EC value of lead contaminated rhizosphere black soil and decreased EC value of red so il rhizosphere.SMS reduced EC values in both soil rhizospheres.Both of them increased the yield of water spinach,but CSMS had a better effect.The addition of remediation agent did not reduce the adsorption of lead on the root surface,and root extrusio n and soil adhesion may be the reasons for this result.The results of high throughput sequencing showed that the effects of remediation agents on the richness and diversity of bacteria in rhizosphere of water spinach in red soil were higher than those in black soil.The composition of the remediation agent,soil p H,EC,lead speciation and root system can affect the microbial population.CSMS can improve soil p H and make the composition of microbial community in red soil evolve to that in black soil.